This invention relates in general to electrostatography and, more specifically, to an improved electrostatographic imaging member comprising a cross linked polyamide coating in an anticurl back layer.
Electrostatographic imaging members are well known. Typical electrophotographic imaging members include photosensitive members (photoreceptors) that are commonly utilized in electrophotographic (xerographic) processes in either a flexible belt or a rigid drum configuration. The electrophotographic imaging member may also be a flexible intermediate transfer belt. The flexible belt may be seamless or seamed. These belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam. These electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer, the photoconductive layer is sandwiched between a contiguous charge transport layer and the supporting conductive layer. Alternatively, the charge transport layer may be sandwiched between the supporting electrode and a photoconductive layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a member such as paper.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers, and an optional overcoating layer. This photoreceptor usually comprises an anticurl back coating on the side of the substrate opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, charge generating layer, charge transport layer and other layers.
After application of the coatings for multilayered organic photoconductors, the resulting web tends to spontaneously curl when the coating solvents evaporate. Curl is primarily due to dimensional contraction of the applied charge transport layer coating from the point in time when the applied charge transport layer coating solidifies and adheres to the underlying surface. Once this solidification and adhesion point is reached, further evaporation of coating solvent causes continued shrinking of the applied charge transport layer coating due to volume contraction. Removal of additional solvent will cause the coated web to curl toward the applied charge transport layer, because the substrate (usually polyethylene terephthalate) does not undergo any dimensional changes. This shrinking occurs isotropically, i.e., three-dimensionally. Curling of a photoreceptor web is undesirable because it hinders fabrication of the web into cut sheets and subsequent welding into a belt. An anticurl back coating layer having a curl equal to and in the opposite direction to the applied layers is applied to eliminate the overall curl of the coated device. However, the anticurl back coating introduces its own problems. The anticurl coating introduces mechanical stresses which, when perturbed by wear, results in distortions resembling ripples. These ripples are the most serious photoreceptor related problem in advanced highly sophisticated imaging machines that demand precise tolerances. When ripples are present, different segments of the imaging surface of the photoconductive member are located at different distances from charging devices, developer applicators, toner image receiving members, and the like, during the electrophotographic imaging process. The quality of the ultimate developed images is thereby adversely affected. For example, nonuniform charging distances can be manifested as variations in high background deposits during development of electrostatic latent images. It is theorized that since the anticurl backing layer is usually composed of material that is less wear resistant than the adjacent substrate layer, it wears rapidly during extended image cycling, particularly when supported by stationary skid plates. This wear is nonuniform, and not only causes the distortions called ripples, but also produces debris which can form undesirable deposits on sensitive optics, corotron wires, and the like. The debris also coats the rollers and creates flatness problems. Ripple formation is due to the critical balance between the stress causing curl, which is established when the xerographically active layers are coated, and the counter stress which develops when the anticurl back layer is coated. Although the photoreceptor lies flat, it is not stress free, but is stress compensated. Wear of the anticurl back layer, especially if that wear is uneven, will cause a deformation in the process direction and that distortion is called ripple.